| OBJECTIVE: To study the surface properties and corrosion resistance of dental cobalt-chromium alloy fabricated by different methods and explore the correlation between them.METHODS:(1)In this study,dental cobalt-chromium alloy was fabricated by different methods(casting,selective laser melting(SLM)and computer aided design/computer aided manufacturing(CAD/CAM)),their microstructure was observed by tungsten filament scanning electron microscope(SEM),surface chemical composition was investigated by energy disperse spectroscopy(EDS),the metallographic structure was observed by metallographic microscope,and the phase structure were analyzed by X-ray diffraction(XRD).(2)The dental cobalt-chromium alloys fabricated by different methods were immersed in pH=2.3±0.2 and 6.8±0.2 artificial saliva(AS)for 1,4,7 weeks,and inductively coupled plasma mass spectrometry(ICP-MS)was used to detect the types and concentrations of major metal ions in the extracted solution.RESULTS:(1)SEM-EDS: the surface of Cast Co-Cr presented diffuse,even corrosion pitting after etching and detected most types of surface chemical element,but SLM Co-Cr showed fine,dense grain and adjacent grain boundary corrosion,and Mill Co-Cr had uniform,smooth surface,fine grain and clear grain boundary,but rare pitting corrosion;Metallographic microscope: the Cast Co-Cr group presented a typical dendritic structure,the SLM Co-Cr group showed a compact cell-like structure,while the Mill Co-Cr group appeared as homogeneous surface and rare dendrite segregation.XRD: all the 3 groups mainly contained face-centered cube(fcc)and close-packed hexagonal(hcp)structure,among which the Mill Co-Cr group had the highest proportion of fcc structure,followed by SLM Co-Cr group and Cast Co-Cr group.(2)ICP-MS: The Cast Co-Cr group was detected most types of metal ions and the total concentration of main ions was highest among different groups after immersed in artificial saliva with different pH and timing,followed by the SLM Co-Cr group and the Mill Co-Cr group.When pH=2.3,the total concentration of ions in the extraction of the three groups first increased and then decreased with time,and the peaks appeared at 4 weeks.When pH=6.8,the total concentration of ions in the three groups kept increasing with time but remained at a low level.CONCLUSION: Metal ions released from casting Co-Cr is larger than that in selective laser melting and milling may due to casting defects,dendrite growth,uneven structure and chemical composition and other reasons,the digital methods shown better chemical stability in immersion corrosion. |
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